There if a long history and developed knowledge of the use of flow forming and related processing for making parts including, cylinders and forming cylinders having internal splines typically formed along the length of the cylinder and perpendicular to the base of the mandrel. Forming and processing to form a variety of such objects, including housings, has been developed and improved over the years.
In general, flow forming offers precision, economy, and flexibility over many other methods of metal forming. The flow forming process typically involves a cylindrical work piece referred to as a “pre-form” or “blank” which can be fitted over a mandrel. In flow forming, the mandrel is a tool on which the preform can be extruded to create an internal mirror shape of the external shape of this tool. In the machine tool, both the pre-form and the mandrel are fixtured and made to rotate while a forming tool applies compression forces to the outside diameter of the pre-form. Typically, the forming tool can include three equally spaced, hydraulically-driven, CNC-controlled rollers or formers. The rollers or formers are successively applied to the pre-form to make a pre-calculated amount of wall reduction during each pass of the roller over the pre-form to form the material toward the mandrel. The material of the preform is compressed above its yield strength, and is plastically deformed onto the mandrel. The desired geometry of the work piece is achieved when the outer diameter and the wall of the preform are decreased and the available material volume is forced to flow longitudinally over the mandrel.
The finished work piece, (i.e., final part) exhibits dimensionally accurate and consistent geometry on the inside of the final part. Subsequent operations can provide the final part a variety of dimensions as desired. The existing flow forming process works well with final parts designed to function as in a clutch housing application since the splines on the inside of the housing holds clutch packs that travel axially in the clutch housing to operate the clutch. Designs such as the clutch housing having straight splines allow for removal of the final part from the mandrel with relative ease since the axis of ejection is coincident to the direction of travel of the mandrel and mandrel adaptor. Generally, it is known to eject a final part including an axially-aligned, straight spline, from the mandrel using a stripper plate. The final part is ejected by moving the mandrel toward a stripper plate which an end of the final part engages while the mandrel continues to be withdrawn from the final part. However, such a process and design has been found to work very poorly when the mandrel is designed to form a axially-offset spline, such as a helical spline, on the pre-form. In these designs, it has been attempted to eject the final part including the helical spline using the same stripper plate and then rotating the mandrel, such as by rotating the main spindle during the stripping process. Such attempts to remove a final part including helical splines have not met with success.
In one failed attempt, part ejection was believed possible by considering the dimensional accuracy of the helical splines of the final part coupled with the traditional final part ejection technique (or system) as well as final part ejection using a rotation of the central ejector counter the direction to that of the main spindle rotation.
Alternatives do exist for making a final part having a helical spline. Such alternatives including processes using traditional broaching and hobbing methods which are multistep, expensive and time consuming processes. These broaching and hobbing techniques generally require a two-part pre-form that is first formed and machined and then the two parts are combined together or integrated into the final part, such as by welding. The current annulus gear vs. the proposed. One such part is generally known wherein the final part is produced using a two-piece construction. A helical ring is broached by a helical broach in each of the two pieces and then they are welded by a laser welder to a pre-machine piece. These generally known techniques were used to form splines in parts for a very long time and flow forming replaced these techniques for parts having straight, axially aligned splines. But the current use of these generally known techniques or systems for final parts having helical splines significantly increases the final and overall costs and inefficiency in creating such a final product. Accordingly, there has long been a need for a technique or system (apparatus and process) to reduce the costs and inefficiencies associated with the broaching and hobbing processes and for forming final parts having a helical spline where the costs and efficiencies are closer to those of using a flow forming technique.
In addition, despite many varied attempts, the flow forming process fails to protect the integrity of the final part and in particular, the dimensional integrity of the helical splines. The traditional broaching and hobbing techniques remain in use but are costly and inefficient. Accordingly, there long remains a significant need for a solution to providing an apparatus and process for stripping a final part having a helical spline from a mandrel while maintaining the integrity of the final part in all aspects.